Development mode for dFlow in Docker

[esune]

The containerized version of dFlow does currently not support hot-reloading of the Angular app. This means that every time a change is made to the frontend, at least the whole Caddy/proxy container needs to be destroyed, build and restarted.

This is a tedious process and reduces the time and productivity when developing the frontend. Adding hot-reloading capabilities would be a big improvement for developers working on dFlow.